Binary phase-scanning antenna with diode controlled slot radiators

ABSTRACT

The present invention relates to an antenna having a plurality of radiators energized to produce radiation in at least two adjacent quadrants and having control means for selectively reversing the phase of radiation of individual radiators to thereby provide direction radiation from the array and to scan such radiation.

United States Patent Inventor Dale C. Lindley Sunnyvale, Calif.

Appl. No. 766,012

Filed Aug. 19, 1968 Patented Sept. 7, 1971 Assignee Textron Inc.

Belmont, Calii.

BINARY PHASE-SCANNING ANTENNA WITH DIODE CONTROLLED SLOT RADIATORS 3Claims, 5 Drawing Figs.

U.S. Cl 343/768, 343/771, 343/854 Int.Cl ..H0lq 13/10 Field of Search343/768,

[56] llelerenees C lted UNITED STATES PATENTS 3,016,535 1/1962 Hewitt343/768 3,056,961 10/1962 Mitchell 4. 343/854 3,085,204 4/1963 Sletten4. 343/777 3,100,300 8/1963 Sletten 343/771 3,175,218 3/1965 Goebels....343/768 3,274,601 9/1966 Blass 343/778 3,392,393 7/1968 Spitz 343/7543,500,251 3/1970 Peace 333/7 Primary Examiner-Eli Lieberman Anomey-Lippincott, Gregg, Hendricson 8t Stidham ABSTRACT: The present inventionrelates to an antenna having a plurality of radiators energized toproduce radiation in at least two adjacent quadrants and having controlmeans for selectively reversing the phase of radiation of individualradiators to thereby provide direction radiation from the array and toscan such radiation.

BINARY PHASE-SANNING ANTENNA WITH DIODE CONTROLLED SLOT RADIATORSBACKGROUND OF INVENTION In many fields such as that of radar it iscommon practice to radiate a highly directional beam of electromagneticenergy and to scan the beam so as to controllably vary the direction ofbeam propagation. It is noted that there have been developed a largenumber of antennas, antenna arrays and antenna feedand control systemsto achieve the above-identified result. It is stated, for example, inU.S. Pat. No. 3,286,260 to Shirly La Var Howard that it is conventionalto employ phase shifting between adjacent elements of an antenna arrayin order to produce scanning of the beam. By incrementally changing therelative phase of energy radiated from successive elements of an array,the direction of a beam from a broadside array, for example, can beshifted. One manner of changing the relative phase of energy radiatedfrom adjacent elements of an array is to vary the frequency of elementenergization. Another manner of electronically scanning a beam from anantenna array is to employ phase-shifting devices between elements forchanging the phase of energy radiated from separate elements. In thislatter category fall ferrite-loaded beam-shifting antennas and the like.The prior art has relied upon some manner of relatively continuouslyvarying the phase between successive elements of an antenna array inorder to electronically scan a beam radiated therefrom, and theabove-noted patent employs both of the phase-shifting techniquesidentified above.

While it is recognized that a directional beam can be electronicallyscanned, it is generally accepted that such scanning requires theutilization of some type of continuous or near continuous phasevariation at each of the radiating elements. This requirement is highlydisadvantageous in necessitating the utilization of relatively complexstructures and circuits.

The present invention provides for the scanning, or controlledvariation, in the direction of propagation of the beam by the selectivereversal of the phase of energy radiated from separate elements of theantenna array. Thus, in accordance with the present invention, it is notnecessary to employ any type of continuous or near continuous phasevariation; there is consequently achieved a material simplification ofstructures and circuits required for electronic-beam scanning.

SUMMARY OF INVENTION The antenna of the present invention comprises aplurality of radiators which may be physically embodied as dipoles,waveguide slots or the like. These individual radiators are energized insome predetermined or random phase relationship which satisfies thefollowing conditions:

I. phase distributed approximately uniformly over at least two adjacentphase quadrants 2. phase of elements of any group of adjacent elementssubstantially different 3. aperiodic phase distribution Selective phasereversal of energy radiated from individual antenna elements is hereinemployed to first produce a desired beam pattern, and second to producea desired scanning of, or change in, such beam. In the followingdescription of the present invention the production of a highlydirectional beam of electromagnetic energy is taken as an example, andthe explanation of the invention is referenced to the production of sucha beam and to the scanning of same, i.e., the controlled variation indirection of propagation. It is, however, to be appreciated that thepresent invention is equally applicable to the generation ofsubstantially any desired beam pattern and to controlled changing of thepattern.

The antenna of the present invention produces an aperiodic phase frontwhich suppresses radiation in other than the desired direction, and itis to be noted that this is quite contrary to conventional systems orantennas normally generating a plane or periodic phase front. Inaccordance with the present invention there is derived a relationshipfor the relative farfield voltage at a predetermined far-field point andcontaining a phase term. It is herein determined that the far-fieldpattern is not determined by a unique set of individual elementexcitation phases, but, instead, is determined by the phase of thealgebraic summation of radiation from a number of elements. Inaccordance herewith the excitation phases of separate elements areconsidered to be distributed in a nonperiodic manner over the range of 0to 21v radians. The phase of each element in the array is then comparedin the value of the phase term as described in more detail below, and ifthe elements excitation phase differs from this value by more than Ir/2radians, the phase thereof is reversed. Consequently, the phase of theresultant of the summation of all elements in a strip statisticallyapproaches the above-noted term as the number of elements is increased.

The present invention may be best described and most easily understoodin connection with a series of linear strips of radiating elements, andis thus so described below. It is, however, to be appreciated that theinvention is equally applicable to circular apertures, as is alsodiscussed below.

DESCRIPTION OF FIGURES FIG. 1 is a schematic illustration bearingnotations employed in theoretical considerations upon which the presentinvention is based;

FIG. 2 is a schematic illustration of an octagonal antenna array inaccordance with the present invention;

FIG. 3 is a partial perspective view of a slotted waveguide as may beemployed in the present invention;

FIG. 4 is a schematic perspective illustration of a dipole radiator asmay be employed in the present invention; and

FIG. 5 is a simple circuit diagram of diode connections for switching inaccordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention may be bestdescribed and understood by initially considering a planar aperturesurface A and radiation in a plane perpendicular thereto. In thisrespect reference is made to FIG. I employing the conventions:

A aperture surface N normal-to-surfacc at some reference point 0 0=angle between the straight lines O-N and 0-? L line on aperture surfacedefined by the intersection of the plane 0 containing the lines ON andOP and the aperture surface S narrow strip on aperture surfaceperpendicular to line L and containing a large plurality of radiatingelements The far-field radiation pattern in plane Q of the array ofradiating elements in FIG. I is determined by the relationship All3E9??? In the foregoing relationship the terms are defined as follows:

E(8)= relative far-field voltage [(d 6) a phase term related to thedifference in path length from the reference point 0 to the far-fieldpoint P and from the aperture point, i, to the far-field point P. Thisphase term is a function of the location of the i" element relative tothe point 0 and of the angle 9. a, complex voltage feeding coefficientfor the element located at position 1'. Consider first that the point,P, toward which the peak of the radiation pattern is to be directed hasbeen chosen. This choice determines the plane, Q, and therefore theintersection line L. This, then, also fixes the orientation of theaperture strips such as S. The orientation of these aperture strips maythus be different for different positions of the main beam peak. Makinguse of the fact that, once the strip orientation has been determined,the elements lying on any strip are equidistant from the far-iield pointP, the relative far-field voltage may be written as:

All All strips elements i 9 ti l.

Phase o f mi: Q g(d,, 6) C(t) All elements in a strip where C(r) is anyspacial constant and may vary with time. In order to satisfy therequirements of the phase relationship set forth immediately above, theexcitation phases of the elements in each strip are considered to bedistributed in a nonperiodic manner over the range of to Zn radians. Thephase of each element is then compared to the value of the right-handterm in the phase equation above corresponding to the strip in which theelement lies. If the excitation phase of the element differs from thisvalue by more than 1r/2 radians, the phase thereof is reversed. Thephase of the resultant of the summation of all elements in a stripthereby statistically approaches g(d, 6) =C(r) as the number of elementsis increase. The amplitude of the resultant approaches It is to beappreciated that the requirements of the phase equation above does notconstrain the distribution of elements within a strip; thus thisdistribution may be made such that the resultant of the summation of allelements in a strip is considerably less than for all points outside ofthe plane Q. By making the distribution different for each strip, it ispossible to further reduce the radiation outside of the plane 0, and bythe proper variation of C(t) it is possible to still further reduce thisradiation. In fact, the maximum minor lobe level can be made to be essentially the same as would be generated by a planar phase-front antennahaving the same amplitude distribution. This is best understood byconsidering the far-field electric field to be composed of twocomponents; one in phase with C(t) and one in quadrature with C(t). Thein-phase components thus produce a radiation pattern with essentiallythe same minor lobe level as would be produced by a planar phase-front.The quadrature components produce a pattern which fluctuates about aspacial average power level given by 1r"',/8n where n number ofelements.

As the value of C(l) is varied, the quadrature pattern maxima and minimaare moved, while the in-phase pattern remains fixed. Therefore, the timeaverage quadrature pattern level approaches the above spacial average atall points in space. This, by increasing the number of elements in thearray, the maximum quadrature pattern level may be reduced to anarbitrary amount below the maximum in-phase or planar phasefront level.

A practical embodiment of the present invention may be constructed bythe provision of a slotted waveguide with individual radiating elementsof the invention being comprised v of slots cut in the broad wall of theguide as schematically illustrated in FIG. 3. Energy is propagated inthe TE, mode through the rectangular waveguide 11, and energy is coupledout of the waveguide through slots formed through the broad wallthereof. There is shown in FIG. 3 one pair of slots 12 and 13 in such awaveguide with the slots of each pair being symmetrically disposed onopposite sides of the center line of the guide. It will be appreciatedthat energy propagated through the waveguide will be coupled out of theguide through these slots, with pairs of slots being spacedlongitudinally along the guide. In accordance with the presentinvention, provision is made for reversing the phase of energy coupledfrom any pair of slots. This is herein shown to be accomplished by thelocation of diodes l4 and I6 in the slots 12 and 13, respectively. Thesediodes are preferably electrically connected in parallel, as illustratedin FIG. 5. Application of a bias voltage in one direction between theterminals 17 and 18 of FIG. 5 will serve to cut off one of the diodes,and oppositely poled bias voltage will cut off the other diode. Thesediodes serve to open or close the waveguide slots for coupling of energyfrom the waveguide.

It is possible in accordance with conventional practice to employ diodesin the manner described above to short one or the other of the slots ofeach pair, so that only the slot which is not shorted will couple energyfrom the waveguide. It is, however, provided in accordance with thepresent invention that the diodes l4 and 16 shall be employed only todetune the slots. with the diodes being employed to controllably shortthe coupling slots, it is necessary for these diodes then to carry arelatively heavy current, but with the diodes placed as shown in FIG. 3at the ends of the slots, it is provided that conduction of a diode onlydetunes the slot, rather than fully shorting it. It will be appreciatedthat a detuned slot does not couple substantial energy from thewaveguide. It is to be further appreciated that employment of the diodesin the manner described above materially reduces the rating required ofthe diodes, so that it is possible to employ much less expensive diodesfor phase reversal herein. It was, in fact, found in one application ofthe present invention that diodes having a normal capability ofoperating at 2 billion Hz., when located at the ends of the waveguideslots as shown, provided fully satisfactory switching at 10 billion Hz.It is considered that this is a marked and novel improvement.

Switching between waveguide slots 12 and 13 of each pair of slots in thewaveguide provides for reversing the phase of energy coupled from eachelement of the waveguide. As noted above, the present invention providesfor beam scanning by selective phase reversal of energy radiated fromindividual elements of a large plurality thereof. Thus, theabove-described slotted waveguide structure with diode switching forselective slot detuning is capable of carrying out the presentinvention.

The slotted waveguide structure described above is only one example ofstructure in accordance with the present invert tion. Insofar asindividual radiating elements are concerned, it is possible to employvarious types and structures. Thus, for example, there is illustrated inFIG. 4 a dipole 21 having quarter-wavelength arms 22 and 23 extendingoutwardly from the outer conductor of a coaxial cable 24 at the upperter minus thereof. This outer conductor is longitudinally slotted fromthe upper end for a distance of one-quarter wavelength to separate theouter conductor into two portions of such length, with one of the anus22 or 23 connected to each side of the outer conductor. Switching isaccomplished with this structure by the provision of a pair of diodes 26and 27 connected between a central conductor 28 of the coaxial cable andthe separate arms 22 and 23. These diodes are preferably connected inparallel as indicated in FIG. 5, so that it is possible with appropriatebiasing to cause either of the diodes to conduct. By the application ofenergizing voltage between inner and outer conductors of the coaxialcable 24, there is thus applied energization to the arms of the dipolewith the phase of such energization being reversible by control of theconduction of the two diodes 26 and 27.

It is also possible to form the present invention as a pair of spacedplates energized, for example, by a probe extending between the platesat the center thereof and probes from in dividual radiating elementsextending through one of the plates at varying distances radiallyoutward from the energizing probe. Various other conventional types ofradiators and radiatonenergizing means may be employed in carrying outthe present invention There is illustrated in FIG. 2 of the drawing anoctagonal array of radiators formed, for example, of strips of radiators31, 32, etc, transversely thereacross, and each of such strips beingcomprised of a plurality of successive individual radiators. Each stripcould, for example, be formed as a waveguide of the type illustrated inFlG. 3, with the individual radiators being then comprised as pairs ofwaveguide slots, as described above. This configuration of FIG. 2provides a substantially circular aperture so that the distribution ofphases in any strip located a given distance from the center of theaperture, for example, will be independent of the location of the pointP at which the beam is to be directed consequently, the far-fieldpattern shape is independent of the choice of the plane Q of FIG. 1.

it is to be understood that the present invention employs a verysubstantial number of radiators or radiating elements, and that theelements of any strip or line thereof are energized to radiate in atleast tow adjacent phase quadrants so that phase-reversal radiation isachieved in all four phase quadrants. Thus it is possible by reversal ofthe phase of radiation from selected elements to produce a desired beamdirection; consequently, by further selected reversals to scan such abeam. With regard to this accomplishment of phase reversal, it is notedthat the preceding description references diode switching; however, itis believed evident that alterna tive types of switching may beemployed. It is furthermore noted that the sequence of diode switching,or phase reversal, and the manner in which such is physicallyaccomplished, is likewise open to wide variation Electronic orelectromechanical means may be employed to control diode switching. Withregard to the establishment of a particular desired beam, it is possibleto locate a radiation source at a point P with phase C(r) toward whichsuch a beam is to be directed and to measure the radiation at eachelement of the invention and then to proceed as described above byreversing the phase of those elements differing from the phase of energyreceived by more than 90. This may be repeated for different locationsof point P throughout a beam scan so as to thus arrive at a phasereversal program, which, when repeated, will direct a beam as desiredand scan same in a desired manner. More practically, the programming ofreversal may be accomplished by a computer.

With regard to the phase of energy radiated from the elements of anantenna array in accordance with the present invention, it is noted thatone highly advantageous arrangement is a random phase distributionbetween elements. It will be seen that any line 4! drawn across thearray of FIG. 2 may be considered as a strip of radiating elements inwhich elements of the strip radiate in all four quadrants of phaserelationship, so that it is possible in accordance with the presentinvention to reverse the phase of particular elements thereof togenerate a beam directed to any far point P. An antenna array of thegeneral configuration of FIG. 2 and having of the order of 400 radiatingelements was employed to produce a highly directional beam which wasreadily and rapidly scanned through a predetermined pattern by thesuccessive reversal of phase of radiation from individual elements ofthe array.

There has been described above an improved and simplified scanningantenna formed of a large plurality of radiating elements energized toproduce radiation in all four phase quadrants and adapted for reversalof phase of radiation from individual elements thereof. In this mannerthere is produced a desired radiation pattern from the array; andscanning of the beam so produced is accomplished by appropriateswitching of the phase of energy radiated by individual elements of thearray. There is also provided hereby an advantageous arrangement forreversing the phase of radiation from waveguide slots by the location ofdiodes at the ends of such slots for detuning a predetermined one of apair of slots located on opposite sides of the center line of awaveguide. Prior art requirements offrequency variation or substantiallycontinuous phase variations for electronic beam scanning are herebyprecluded.

Although the present invention is described herein with respect toparticular preferred embodiments thereof, it is not intended to limitthe invention to the exact terms of description or details ofillustration, but, instead, reference is made to the appended claims fora precise delineation of the true scope of this invention.

That which is claimed is:

1. An improved antenna comprising a large plurality of radiatingelements aligned in strips, each strip comprising a waveguide havingpairs of slots therein with the slots of each pair being diametricallydisposed on opposite sides of the center of the waveguide and diodesconnected across each slot, means energizing said elements to radiateenergy in at least two adjacent phase quadrants with the phase ofelements of any group of adjacent elements substantially different andestablishing a nonperiodic phase distribution across the array, andswitching means selectively reversing biasing of diodes of each pair ofslots for selectively reversing the phase ofenergy radiated by eachradiated element to thereby establish a predetermined radiation beampattern and further successively reversing the phase of predeterminedelements in predetermined order to change the direction or pattern of aradiated beam in a preselected manner.

2. The antenna of claim 1 further defined by said diodes being disposedacross ends of said slots for selectively detuning said slots from saidwaveguide.

3. In an antenna structure having at least one waveguide with couplingslots in the wall thereof for coupling waveguide energy to theatmosphere, the improvement comprising each waveguide having pairs ofslots spaced along the length thereof with the slots of each pairdisposed equidistant on opposite sides of the center of the waveguide,diodes connected one across the end of each waveguide slot with thediodes of each pair of slots being connected in parallel opposed arrangement and being controllably biased by opposite polarity voltage causingeither one only of each pair of diodes to conduct for selectivelyreversing the phase ofenergy coupled to the at mosphcre from each pairof slots.

1. An improved antenna comprising a large plurality of radiatingelements aligned in strips, each strip comprising a waveguide havingpairs of slots therein with the slots of each pair being diametricallydisposed on opposite sides of the center of the waveguide and diodesconnected across each slot, means energizing said elements to radiateenergy in at least two adjacent phase quadrants with the phase ofelements of any group of adjacent elements substantially different andestablishing a nonperiodic phase distribution across the array, andswitching means selectively reversing biasing of diodes of each pair ofslots for selectively reversing the phase of energy radiated by eachradiated element to thereby establish a predetermined radiation beampattern and further successively reversing the phase of predeterminedelements in predetermined order to change the direction or pattern of aradiated beam in a preselected manner.
 2. The antenna of claim 1 furtherdefined by said diodes being disposed across ends of said slots forselectively detuning said slots from said waveguide.
 3. In an antennastructure having at least one waveguide with coupling slots in the wallthereof for coupling waveguide energy to the atmosphere, the improvementcomprising each waveguide having pairs of slots spaced along the lengththereof with the slots of each pair disposed equidistant on oppositesides of the center of the waveguide, diodes connected one across theend of each waveguide slot with the diodes of each pair of slots beingconnected in parallel opposed arrangement and being controllably biasedby opposite polarity voltage causing either one only of each pair ofdiodes to conduct for selectively reversing the phase of energy coupledto the atmosphere from each pair of slots.